Concentration of isomeric diolefins



Patented Sept. 12, 1944 CONCENTRATION OF ISOMIEBIC DIOLEFINS Richard F. Bobey, Roselle, and Herbert K. Wieae, Union, N. 1., assignorl, by meme assignments,

to Jasco, Louisiana Incorporated, a corporation oi No Drawing. Application October 11, 1941, Serial No. 414,836

7 Claims.

This invention relates to the separation and concentration of isomeric dioletlns and particularly to the concentration and isolation 01' a cisdiolefln.

Piperylene (1,3-pentadiene) is a first in the homologous series of conjugated diolefins to exist in two geometrical isomeric forms. Since these two isomers possess different details of chemical activity in some reactions, it is desirable-to be able to concentrate the individual forms.

An object of this invention is to separate cispiperylene from trans-piperylene.

Another object of this invention is to separate cis-piperylene from other hydrocarbon compounds particularly those present in a cracked petroleum fraction.

According to this invention the conjugated dioleflns present in hydrocarbon fractions are preterably first concentrated to substantially complete exclusion of other types of hydrocarbons. This concentration is preferably carried out by the use of a process which-does not promote isomerization of cis-diolefins to trans-diolefins. Such a process is in the use or solid cuprous salts as extractants. The initial diolefin fraction is preferably derived from a high temperature source such as the cracking of gas oil or the thermal or catalytic dehydrohalogenation of the higher dihaloalkanes. In any case the purified conjugated diolefln mixture is submitted to reaction under appropriate conditions with a reagent capable of undergoing the so-called Diels-Alder condensation with conjugated diolefins, whereby the trans-diolefin reacts substantially completely to form unsaturated cyclic compounds; however, it has been found that the cis-isomer reacts slowly, ii at all, with these reagents and therefore remains in substantially pure form as a recoverable residual hydrocarbon.

This invention relates particularly to the separation of pure cis-piperylene from its mixtures with transpiperylene. It also relates particularly to the use of maleic anhydride as the Diels-Alder condensing agent, but it has been shown that the process is applicable to higher diolefins and to other condensing agents.

The two isomers of piperylene have a molecular structural diflerence which may be represented in one plane as:

CH; CH1 H H0 mtg 114 on, OH HO- Gfig Trans-isomer cis-isomer Now since the Diels-Alder condensation with maleic anhydride involves a closure to form a six-membered ring. an explanation or the sliderence in reactivities of the cisand trans-isomers of the dioletln might lie in the interference otthe protruding methyl group of the cis-isomer in the ring closure. Thus, the trans-form reacts readily, l

CH3 CE: HO 110-0 0 CH-O 0 B 0 y 0 I CH HU-CO /UHC0 I CHI CH Ca Trans-piperylene+malgigtgguhgdigggmzv methyltetrahydrowhile the cisfails .to give any appreciable condensation.

no-co no b 0 no reaction 11 on \C Eu-CO With regard to the conjugated diolefins containing more than five carbons, the invention is applicable to compounds having the following general structure and also capable of existing in the form of two geometrical isomers:

R: I where R1 is alkyl or aryl, but preferably methyl, R: and R: are hydrogen, alkyl or aryl. The geometrical isomer inactive to Diels-Alder condensation is the form in which the ethenyl group is cis with respect to R1 and which we arbitrarily term the cis-isomer.

Example I 'tures, boiling between 37 and 45 C., and substantially free of cyclopentadiene was treated with cuprous salts in an appropriate manner whereby piperylene was concentrated in substantially pure Iorm as a mixture of its 015- and transisomers. The high purity of this fraction was vouched for by its index of refraction and by its reaction with two moles of hydrogen per mole.

The purified piperylene was then vaporized into a stream of hydrogen and the resulting mixture was dispersed and caused to pass through a body of molten maleic anhydride maintained at C., after which the gas wasireed oi entrained material and passed through a condenser at -78 C. Thereby the unreacted piperylene was condensed andcollected. The collected residue had most of the chemical properties of piperylene but diflered in that it was virtually unreactive with Diels-Alder condensation reagents, particularly maleic anhydride. The properties of the orig- 

